COLUMBA. 369 



the special points to notice are as follows: — (i) The 

 cerebral hemispheres are large and reach the 



ervoTis. (.gj.g|3giium posteriorly, hence the optic lobes 

 are lateral in position. (2) The whole of the brain lies 

 behind a line drawn through the eyes. (3) The olfactory 

 lobes are very small and poorly developed. 



The skeleton of the pigeon is as remarkably 

 modified as is the rest of its anatomy. 



In the skull we may note the complete fusion of the 

 cranial and some of the facial bones, leaving no sutures. 

 The upper beak is supported chiefly by the premaxillce and 

 by the maxillce^ the thin jugal joining the maxillae with the 

 quadrate posteriorly. Further, towards the middle ventral 

 line the two palatines pass back from the maxillae to meet 

 \hQ pterygoids which pass outwards and backwards to join the 



Fig. 261. — A Cervical Vertebra of the Pigeon. {Ad nat.) 



■■ Neural Crest. 

 ^ Neural Canal. 



Cervical Rib. 



Heterocoelous Facet. 



.Vertebrarterial 

 Canal. 



quadrates. Each quadrate has a condyle for articulation with 

 the mandible bearing the lower beak ; they are freely movable 

 upon the skull. All the other bones are fused. 



The orbits are very large and are separated by a thin 

 septum only partially ossified, the interorbital septum. Its 

 ventral edge, under the palatopterygoid junction, is thick- 

 ened and forms the rostrum. 



The septum is said to be formed of the mesethmoid and presphenoid 

 of the rabbit, whilst the rostrum is supposed to be homologous with the 

 anterior part of the frog's parasphenoid, the posterior part of which is 

 represented by the paired basitemporah ventral to the basisphenoid. 



There are three ear-bones but the pro-otic alone remains free, the 

 others fusing with the occipital bones. 



There is a single occipital condyle on the basisphenoid 

 and the mandible is ossified into five bones. -- 



M. 25 



